The present invention represents an improvement over the apparatus disclosed in U.S. Pat. No. 3,685,756, of Marx et al., titled "Method and Apparatus for Slitting Belt," issued Aug. 22, 1972. This patent should be carefully considered in order to put the present invention into proper perspective.
Presently, conveyor belt material is manufactured in a single width (usually two or three meters) and then is slit longitudinally, as necessary, to provide conveyor belting of narrower widths. This is true regardless of whether the conveyor belting is heavy duty "black" belt used for handling and conveying heavy or course materials, or lighter weight "white" belt used for handling lightweight items or food products.
A large roll of uncut belting material, sometimes referred to as a slab, can weigh between 10,000 and 30,000 pounds. Consequently, handling of this material through a slitting apparatus can be cumbersome and difficult to control. Most of these difficulties are due in large part to the sheer weight of the roll of material being handled. For example, very high torque is required to wind and unwind such a roll of belting material. Once such a roll has been set into motion, the inertia of its mass makes it equally difficult to stop with precision. Likewise, lateral repositioning of such a roll in order to maintain a uniform cut width also presents difficulties. Despite these difficulties, precise slitting is imperative.
In general, with the apparatus disclosed in the previously-mentioned '756 patent, an unslit roll of belt is carried on a first spindle, and the subsequently-slit belt is wound onto a second spindle. Between the two spindles, is the cutting apparatus having one or more cutting blades spaced laterally along the cutting apparatus. A series of rollers feed the belting material past the cutting blade. The rollers are responsible for pulling and pushing the belt material past the cutting apparatus, thereby maintaining even longitudinal and lateral tension on the web of belt.
Manufacturers of belting material have found that belting material can be more economically produced in wider widths. As previously discussed, these widths can be as great as four meters, compared to previous standard widths of approximately two meters. This increase in width accounts for the proportionate increase in weight for a roll of belting material of a given length. Despite the increased production width of belting material, the core onto which such belting is rolled has not changed substantially.
Pursuant to industry standard, conveyor belting is rolled onto a cylindrical core having a square-shaped axial passageway. A square core bar is inserted through the passageway of the core to act as a spindle on which the roll can be supported. The square shape of the core bar allows the roll to be driven by hydraulic motors or the like.
With three-meter wide belt, it is not unusual that a roll will tend to sag under its own weight (up to 10,000 pounds) when the core bar is supported only at opposite ends. This tendency to sag is complicated by the fact that the core bar has a square cross-sectional shape. When the core bar is positioned such that upper and lower sides of the square are horizontal and lateral sides are vertical, the bar is more susceptible to more bending than when the bar is rotated 45.degree. therefrom. When the core bar is rotated 45.degree., each panel of the core bar is positioned diagonally relative to horizontal. In other words, as the core bar is rotated from a position in which its cross section is "square" to a position where its cross section is "diamond-shaped," its ability to resist bending changes. This is due to the effective change in vertical dimension of the core bar from one position to the other. Consequently, a roll of belting material can tend to "wobble" between positions of lesser and greater sag as it is rotated on the spindle of the slitting apparatus. This wobble causes undesired fluctuation in the tension of the belt as it is being slit, making subsequent control of the belt at the cutting apparatus more difficult.
Wobbling also complicates the coupling of the end of a core bar to a drive motor. As the central portion of the core bar sags, the outer ends of the core bar rise, because bearings support the core bar at points spaced inwardly from the core bar ends. The coupling of a drive motor to a vertically-oscillating core bar end can be difficult when the load carried by the core bar is relatively heavy. The previously-described sagging and "wobble" effect becomes significant as the weight and diameter of the outfeed roll increase.
Another problem encountered when two or more webs of slit belting material are subsequently wound onto the same spindle is that minute lateral shifting of the webs will cause the slit ends of the web layers to overlap slightly a previous layer, thereby making separation of the slit webs extremely difficult.
It is an object of the present invention to address these and other problems existing in prior art belt-slitting devices. The solutions provided by this invention will become apparent upon the reading of the following specification, drawings, and claims.